Concepts of low dielectric constants integrated with low interconnect resistance metal structures have been proposed by many technologists. Those ideas include "pillar plugs", "anti-contacts/vias", spin-on-low-dielectric-constant insulators (either organic and/or inorganic), spin-on layered low dielectric constant materials and technology, damascene of metal interconnects and dual damascene of metal interconnects. By "damascene" is meant a process in which trenches or contact/via openings are formed and then filled with metal using CVD (chemical vapor deposition) or PVD (physical vapor deposition) or other techniques, followed by a polish to remove any overfilled areas. The term is based on a process developed by goldsmiths in ancient Damascus, comprising crafting a pattern or design on a hard surface and then hammering fine gold wires onto the designed pattern.
Many ideas have been proposed for combinations of low dielectric constant and low interconnect resistance metal structures, but none have been introduced into commercial practice at this time. The only demonstration of these new advanced concepts is work done by IBM on BPDA-PDA integration with copper interconnects. "BPDA-PDA" refers to a polyimide available from E.I. du Pont de Nemours, under the trade designation PI-2610. The BPDA-PDA is intended to replace silicon dioxide. However, since copper is a source of contamination, then special care has to be taken to prevent copper from diffusing into other parts of the IC structure and causing failures. This is done by using a Si.sub.3 N.sub.4 layer to separate the copper layer and the BPDA-PDA layer. However, Si.sub.3 N.sub.4 has a dielectric constant of about 8, which increases capacitance over that of structures employing silicon dioxide. Further, a barrier metal, comprising approximately 1000 .ANG. of refractory metal cladding is added, which increases the interconnect resistance. While this technology employs very advanced processing techniques such as dual damascene and chemical vapor deposited (CVD) copper and provides reliable interconnects, nevertheless, the final result is a very minor improvement over the existing system. The composite dielectric constant of BPDA-PDA is about 3.8 and the copper/refractory metal has a composite resistance of about 2.6 .mu..OMEGA.-cm, as compared to the conventional SiO.sub.2 dielectric and Al interconnect (4.0 dielectric constant and 2.8-3.2 m.OMEGA.-cm resistance, respectively). The slight improvement in overall capacitance and resistance is achieved at a high process cost, and thus is not cost-justified.
Thus, there remains a need for providing a comparatively simple process that results in increased device speed.